The present invention relates to an electrically operated heating element for a hot-runner tool that has a heat conductor and is positioned in a hot runner and in runners that derive from the heat conductor and lead to a series of outflow channels from the hot-runner tool.
A hot-runner tool with an electrically operated heating element is known from AT-PS No. 286 607. Its heat conductor is a rod or wire and is positioned in the center of the tool runner tool where it forms a loop in the vicinity of the runners that derive from the hot runner. The flanks of the loop extend along the inside of the runners. One drawback of the known hot-runner tool is that the rod-shaped or wire-shaped conductor can deform as a result of the impact of molten plastic entering the hot runner and come into contact with the surfaces of the hot-runner tool. This contact causes an immediate short circuit and downtime.
Furthermore, since the heat conductor has the same cross-section at all points, the same amount of heat will be generated at every point.
Since the heat conductor forms a loop in the vicinity of one runner and the loop can only be employed in runners with relatively large diameters, the known hot-runner tool cannot be employed for an injection mold in which the feed apertures in the mold nests are slightly separated and in which small parts are cast.